(1) Field of the Invention
The present invention relates to a toner having a deformed spherical shape of substantially a same particle size, an easy method for obtaining same, and an imaging apparatus using same. The term "deformed" here means "processed for having a shape of other than a substantially exact sphere", and the same hereinafter.
(2) Description of the Prior Art
Solid ink called toner is widely used in image forming methods such as electronic photograph, and electrostatic recording method etc. As for a general method for manufacturing the toner, a method has been used in which resin and additives such as coloring agents are mixed together, the mixture is pulverized into particles having small diameters, and subsequently the particles are classified in order to obtain particles having adequate diameters.
Currently, so-called polymerized toner capable of being manufactured without the pulverization and the classification has widely been studied (JP-A-57-154253 (1982)). The polymerized toner is manufactured without the pulverizing operation after polymerization of the resin by controlling a particle size distribution to an adequate one for toner particles when the resin is produced by a suspension polymerization method or an emulsion polymerization method.
The toner particles obtained by the above methods have a narrower particle size distribution than that of the particles obtained by the pulverization method, and accordingly, the classification of the particles is not necessary.
Further, the toner particle obtained by the above method has a smaller surface area than that of the toner particle obtained by the prior art, and accordingly, the toner particle has an advantage of being small hygroscopic.
When the toner is manufactured by a polymerization method, the process has the steps of polymerizing the resin, settling the particles by centrifuging, removing dispersing agents by repeating the settling and decanting after adding water to the particles, and drying the particles. The above described process is complex in its operation, and is more disadvantageous in necessary time and cost than the conventional pulverization method.
Further, the particles obtained by the polymerization method have a problem that the particle is substantially an exact spherical shape, although the particles have a relatively same diameter. When the particle is an exact sphere, the particle has a small surface area, and has had a problem for being used as a toner such as a poor charging property because of a very small contacting area with a developing object, e.g. a drum and paper, at a developing operation.
In order to overcome the above described problem, a several methods for deforming the particles are studied. For example, a method wherein a fine particle obtained by another polymerization method is attached to the particle obtained by the above polymerization method (JP-A-1-10263 (1989)), and methods for obtaining deformed particles by pulverizing the particles obtained by the polymerization method with giving physical impact by a ball milling and so on have been proposed. However, all of the example methods have a problem that the toner particles having substantially a same diameter are very difficult to be obtained without the classification because the attached fine particle in the former case and generated fine particles by the ball milling in the latter cases expand a width of their particle diameter distribution.